linux-kernel - Re: [PATCH 2/2] fat (exportfs): reconnect file handles to evicted inodes/dentries

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Date:	Tue, 10 Jul 2012 04:10:00 +0900
From:	OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
To:	"Steven J. Magnani" <steve@...idescorp.com>
Cc:	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/2] fat (exportfs): reconnect file handles to evicted inodes/dentries

"Steven J. Magnani" <steve@...idescorp.com> writes:

>> > >> > Interesting idea. I think this, and reformulating the FAT NFS file
>> > >> > handle to include the parent's i_ino, will greatly simplify (and speed
>> > >> > up) the code.
>> > >> 
>> > >> Does it work even if the inode was rename()'ed?
>> > >
>> > > AFAICT. I don't see why it wouldn't; on a rename, the inode's i_pos
>> > > changes but its i_ino stays the same, right?
>> > 
>> > If the inode is not on cache anymore, is there the possibility that
>> > selects the wrong parent? IIRC, NFS Server can be rebooted at any time
>> > while the client using the same file handle.
>> 
>> True, but it's looking like we can just use the default handle
>> constructed by export_encode_fh(), namely (i_ino, i_generation,
>> parent->i_ino, parent->i_generation). None of those components should
>> change in a server reboot.
>
> I think I misunderstood you when I wrote this. I assumed we were talking
> about a restart of nfsd, not the entire machine it was running on. If
> there is a danger of mismapping on a reboot isn't that present in the
> existing mainline code, i.e. fat_fh_to_dentry()? Ideally, the (i_ino,
> i_generation) signature would be different on a reboot, although with
> only 2-second granularity in i_generation I suppose that's less likely
> than we would prefer. Also I would think that many inodes simply
> wouldn't exist in the cache, in which case we would fail the operation
> with ESTALE.

Ah, i_ino. I was talking about i_pos. Well, so, what happens if the
child was renamed to other parent on NFS server machine (not via nfs
client)? The file handle would be including the old i_ino, and the old
i_ino on file handle is still vaild as old parent. So, it returns the
wrong parent?
-- 
OGAWA Hirofumi <hirofumi@...l.parknet.co.jp>
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